An Australian pilot had the shock of his life when he saw a snake in his cockpit, but the situation worsened when the reptile crawled across his leg forcing him to make a harrowing landing.

Braden Blennerhassett, 26, didn't know if the snake was deadly but his heart raced as he tried to hold the cargo plane steady, worried that even that behaviour would trigger the reptile to strike.

"I've seen it on a movie once, but never in an airplane," Blennerhassett told Australian Broadcasting Corp., referring to the 2006 movie "Snakes on a Plane," in which deadly snakes are deliberately released in an airliner as part of a murder plot.

The Air Frontier pilot was alone in a twin-engine Beechcraft Baron G58 and had just left Darwin airport on a cargo run to a remote Outback Aboriginal settlement when he saw the snake on Tuesday.

Blennerhassett decided to return to the Darwin airport after spotting the snake popping his head out from behind the instrument panel.

The situation intensified when, during the approach to the airport, the snake crawled across his leg.

Air Frontier director Geoff Hunt described Blennerhassett as a "cool character" who radioed air traffic control to report: "I'm going to have to return to Darwin. I've got a snake on board the plane."

Blennerhassett told Nine Network television he was "shaken" and that his heart rate and blood pressure were "a bit elevated."

"You're trying to be as still as you possibly can and when you've got your hands on the power levers," he told ABC. "You're kind of worried about the snake taking that as a threat and biting you."

"As the plane was landing, the snake was crawling down my leg, which was frightening," he told Nine.

When the plane landed, a firefighter spotted the reptile but wasn't able to catch it. A trap baited with a mouse didn't work either by Thursday and the aircraft remained grounded.

Wildlife ranger Sally Heaton said the snake was likely a golden tree snake, a non-venomous species that can grow up to 1.5 metres.

Blennerhassett was back in the air Thursday and couldn't be reached for comment.

Hunt said he wasn't aware of a snake being found in a plane before in Australia.

He had heard of a young chicken being found alive under the floor of a plane, and of an escaped juvenile crocodile crawling under a pilot's rudder pedal.